1. Field of the Invention
The present invention relates to a clamping apparatus for a press brake, adapted to perform the fixing or the fixing cancellation of an upper-die relative to a ram of the press brake by means of a hydraulic operation in the press brake employed for a bending process and the like of a long-sized plate.
2. Prior Art
Hydraulically operated upper-die clamping apparatuses are known in the art as disclosed in Japanese Utility Model Laid Open Publication No. 1989-49318.
This apparatus comprises a clamping receiving member disposed on the back side of a ram lower portion, a clamping press member composed of a plurality of clamping press plates arranged side by side in the left and right direction on the front side of the ram lower portion and a clamping hydraulic cylinder internally disposed in each of the press plates. The upper-die to be butted to the ram lower portion from below is adapted to be fixedly secured between the clamping receiving member and the press plates by means of hydraulic forces of the respective hydraulic cylinders.
Pressurized oil supply/discharge ports connected in communication to an operating oil chamber of the hydraulic cylinder are opened in the upper surface of each press plate. The adjacent pressurized oil supply/discharge ports are interconnected to each other in sequence by means of a reversed U-shaped hydraulic pipe running along the space in front of the ram.
In the above-mentioned prior art, since the hydraulic pipes are arranged in such a manner so as to project into the space in front of the ram, a working space for bending a long-sized work plate becomes narrowed by that projecting distance. Further, in such prior art, it is possible that the hydraulic pipes could be broken and damaged by the bent work plate.